1. Field Of The Invention
This invention relates to distribution type fuel injection pumps, and more particularly to such pumps where a spring biased electromagnetically driven, axially slidable cut off sleeve varies the quantity of the individual fuel injection directed to the engine cylinders.
2. Description Of The Prior Art
The present invention relates to a distribution type fuel jet pump of the type set forth in U.S. patent application Ser. No. 274,655 filed July 24, 1972, now abandoned and entitled FUEL INJECTION PUMP.
In such distribution-type fuel injection pumps, a drive shaft rotated by an associated engine causes by way of a rotatable and axially shiftable cam disc, a cylindrical plunger to follow the rotational and reciprocating movement of the cam disc, the plunger being mounted for axial movement and rotation within a fixed plunger barrel. A cylindrical cut off sleeve is slidably and concentrically mounted on the plunger to the side of the fixed plunger barrel opposite that of the cam disc. A cylindrical closure plug is slidably mounted within the cylindrical cut off sleeve and defines a compression chamber between one end of the closure plug and the end of the axially slidable and rotatable plunger which supports the cut off sleeve. The cut off sleeve abuts a fixed cylindrical magnetic core member about which is concentrically mounted a slidable electromagnetic coil which is fixed to the cut off sleeve and drives the sleeve axially against the bias of a compression spring and in a direction tending to reduce the compression chamber formed between the closure end plug and the end of the axially slidable and rotatable plunger. A plurality of radial channels sequentially align with a fuel inlet channel, a fuel outlet channel and a cut off channel respectively, all of which are in communication with the compression chamber 25 by way of a central channel common thereto and extending axially throughout a portion of the plunger. A low pressure pump delivers fuel from a fuel tank compressed to a value corresponding to the rotary speed of the engine to the supply port of the inlet channel. Simultaneously, the cam disc and plunger are rotated synchronously so that the plunger is imparted with a reciprocating movement corresponding to the lift of the cam face. During the plunger's movement axially back and forth, the suction port comes into registry with the inlet channel of the barrel whereby a portion of the liquid fuel which has reached the supply port is transferred to the compression chamber 25 through the central channel. On further movement of the plunger to reduce the volume of the compression chamber, the radial chamber shifts from a position of alignment with the inlet channel and a second radial channel aligns itself with the outlet channel and the fuel already compressed in the compression chamber is injected under the resulting pressure to one of the cylinders of the engine through a delivery channel. The continued axial shifting of the plunger towards the relatively axially fixed closure end plug continues to reduce the size of the compression chamber until a further radial channel registers with the cut off channel communicating the compression chamber to a low pressure oil sump. This identical action takes place cyclically for as many times as the number of engine cylinders are used for a single rotation of the drive shaft.
Fuel metering is effected by axial shifting of the cut off sleeve which adjusts the timing of the fuel which overflows from the cut off port to the oil sump in relation to the lift of the plunger.
In this respect, an electromagnetic coil acts as a movable solenoid coil which shifts axially back and forth at the same time driving the cut off sleeve, while the closure end plug slides relative to the cut off sleeve maintaining its contact with the fixed core of the assembly. With the coil de-energized, the sleeve is shifted axially to its fullest extent towards the drive shaft and the cam disc. Thus, the axially shiftable and rotatable plunger must shift axially towards the fixed core driven by the cam disc to its minimum extent to align the radial channels and the cut off channel within the cut off sleeve, thus terminating the quantity of fuel injected to the engine and permitting the compressed fuel within the compression chamber to drain to the oil sump. Upon energization of the electromagnetic coil to its maximum extent, the electromagnetic coil and thus the cut off sleeve is shifted in the direction of plunger movement to delay the time at which the cut off channel is aligned with its associated radial channel within the plunger open to the common axial channel, which in turn permits the compression chamber to drain to the sump, thereby increasing the quantity of fuel being injected to the cylinder or cylinders. Effectively, the quantity of fuel injected to the respective cylinders of the engine may be varied electrically in response to electrical signals from various control elements such as an induction coil of a signal generator whose pulse voltage is proportional to the rpm of the engine, electromagnetic detection of the displacement of the accelerator pedal or a feed back signal representive of the axial position of the cut off sleeve.
In such distribution type fuel injection pumps having a plunger barrel within which an axial and rotatable plunger is fitted and which, in turn, supports an axially slidable cut off sleeve which is subjected to the forces of a control spring and electromagnet acting in opposition for decreasing the quantity of the fuel injection and for increasing that quantity respectively, although the cut off sleeve is restored by the force of the spring and by the electromagnet, respectively, depending upon the increase or decrease in the electrical current flowing to the coil which acts to displace the sleeve relative to the core, because of the sliding resistance between the plunger and the cut off sleeve, there is a tendency for the following injection stroke to being prior to the restoration of the sleeve to its original position and as the pressurized fuel is cut off from the pump outlet channel and directed from the compression chamber through the common channel to the fuel pump. For this reason, the position of the cut off sleeve and thus the quantity of the injection fuel for each pulse jet output of the pump becomes unstable regardless of the fact that the electromagnetic force of the coil during ordinary operation remains constant and also that of the displacement of the cut off sleeve as the fuel is injected to each of the cylinders so that the deviation in the quantity of fuel injection to each of the cylinders becomes relatively large.
It is thus an object of the present invention to eliminate the above drawbacks and reduce the amount of axial displacement of the cut off sleeve at the cut off period created by the sliding resistance between the plunger and the cut off sleeve by providing a dash pot chamber between the plunger barrel and the cut off sleeve.